System and method for controlling pump performance in a transmission

ABSTRACT

The present disclosure provides a hydraulic system of a transmission having a controller and a variable displacement pump. The pump includes an inlet and outlet and is adapted to be driven by a torque-generating mechanism. The system also includes a lube circuit fluidly coupled to the pump. A lube regulator valve is disposed in the lube circuit, such that the lube regulator valve is configured to move between at least a regulated position and an unregulated position. The regulated position corresponds to a regulated pressure in the lube circuit. A pressure switch is fluidly coupled to the lube regulator valve and configured to move between a first position and a second position, where the switch is disposed in electrical communication with the controller. A solenoid is disposed in electrical communication with the controller and is controllably coupled to the pump to alter the displacement of the pump.

FIELD OF THE DISCLOSURE

The present disclosure relates to a transmission control system, and inparticular, to a system and method for controlling pump performance in atransmission.

BACKGROUND

In a conventional powered machine, a prime mover can operate atdifferent speeds and produce different levels of power that istransferred to a transmission. In one instance, the prime mover can bean engine. In turn, the transmission can transfer torque to a drivelineor final drive assembly, which can be directly mounted to the wheels ortracks of the powered machine. The transmission can include an internalpump that is rotatably driven by the prime mover, and based on thedifferent speeds of the prime mover, the pump can produce differentlevels of fluid flow and pressure. In some instances, there is only oneinternal pump in the transmission that provides fluid flow to a mainpressure circuit and lube circuit of the transmission.

A conventional hydraulic pump is often designed as a result of itsdesired functionality. In an engine-transmission application, forexample, a conventional hydraulic pump may be designed for one ofseveral reasons, namely, 1) to provide adequate fluid flow at a lowengine idle speed (e.g., approximately 500 RPM), 2) to provide fullregulated pressure to the main pressure circuit of the transmission at aspecific engine speed (e.g., approximately 1000 RPM), and/or 3) to filla transmission clutch within a desired time period (e.g., approximately200 ms at 1200 RPM). Other design considerations may include margin ofsafety and leakage at a fluid temperature of about 120° C. In view ofthe different design considerations accounted for in a hydraulic pump,however, the pump still often tends to overproduce fluid flow at orabove normal operating conditions and engine speeds.

Moreover, once the hydraulic pump is able to provide adequate fluid flowto the control and lube systems of the transmission, additional fluidflow produced by the pump is generally returned to transmission sump andis unusable. This excess fluid flow, however, directly contributes tohydraulic spin-loss inside the transmission. In effect, this reducestransmission productivity and performance.

One possible solution to the excess flow produced by the hydraulic pumpis to incorporate a variable displacement pump into the transmissiondesign. A variable displacement pump can increase or decrease volumeinside the fluid cavity of the pump, thereby controlling the pumpdisplacement and production of fluid flow. By controlling displacement,the pump can produce a more desirable amount of flow under steady-stateconditions. When the transmission is in a certain range, for example,the hydraulic demand is usually fairly low and the volume of the oilcavity can be decreased, thereby resulting is reduced overall pump flow.Likewise, during a shift between ranges, the hydraulic demand increasesfor filling a clutch such that the volume of the oil cavity is increasedand more flow is produced to meet demand.

Since the “decrease” pressure is based off of pressure in the maincircuit, however, there is an inherit response time drawback. In otherwords, the demand to increase fluid flow (e.g., when filling a clutch)begins before the volume of the pump cavity increases (“decrease”pressure responds). Thus, regardless of what improvements are made tothe pump and transmission system, the hydraulic demand rises before thepump can supply the desired flow, thereby resulting in an undesirabletime delay to fill the clutch. This can impact fuel economy and shiftquality.

A need therefore exists for electronically controlling the pump capacityof the transmission. By controlling pump capacity, it is also desirableto control fluid flow from the pump to minimize excess flow once thedifferent fluid circuits of the transmission are satisfied, improveshift quality, and control fluid temperature of the transmission.

SUMMARY

In an exemplary embodiment of the present disclosure, a hydraulic systemof a transmission includes a controller and a variable displacementpump. The pump is adapted to be driven by a torque-generating mechanismand includes an inlet and an outlet. Moreover, the pump is configured togenerate fluid flow and pressure throughout the system. The system alsoincludes a main circuit fluidly coupled to the pump and a main regulatorvalve disposed in the main circuit. The main regulator valve isconfigured to move between at least a regulated position and anunregulated position, where the regulated position corresponds to aregulated pressure in the main circuit. A pressure switch is fluidlycoupled to the main regulator valve and configured to move between afirst position and a second position, where the switch is disposed inelectrical communication with the controller. A solenoid is disposed inelectrical communication with the controller, such that the solenoid iscontrollably coupled to the pump to alter the displacement of the pump.

In one aspect of this embodiment, once the fluid pressure in the maincircuit reaches a substantially regulated condition, the main regulatorvalve moves from the unregulated position to the regulated position. Inanother aspect, the pressure switch is configured to detect the movementof the main regulator valve between the regulated position andunregulated position and the pressure switch moves between the firstposition and the second position upon movement of the main regulatorvalve. In a further aspect, the movement of the pressure switch betweenthe first position and second position induces a signal triggered to thecontroller such that the controller controllably actuates the solenoidbased on the signal. In yet a further aspect, the pump displacement iscontrollable between a first displacement and a second displacement,where the fluid flow distributed from the outlet is adjustablycontrolled based on the pump displacement and the actuation of thesolenoid controllably adjusts pump displacement.

In a different aspect of this embodiment, a lube circuit is fluidlycoupled to the pump and main circuit and a lube regulator valve isdisposed in the lube circuit. The lube regulator valve is configured tomove between at least a regulated position and an unregulated position,where the regulated position corresponds to a regulated pressure in thelube circuit. A second pressure switch is fluidly coupled to the luberegulator valve and configured to move between a first position and asecond position, where the second pressure switch is disposed inelectrical communication with the controller.

Related thereto, the lube regulator valve moves to its regulatedposition after the main regulator valve moves to its regulated position.Moreover, the lube regulator valve moves from the unregulated positionto the regulated position once the fluid pressure in the lube circuitreaches a substantially regulated condition and the second pressureswitch is configured to detect the movement of the lube regulator valvebetween the regulated position and unregulated position, where thepressure switch moves between the first position and the second positionupon movement of the main regulator valve. Further related thereto, themovement of the second pressure switch between the first position andsecond position induces a signal triggered to the controller and thecontroller controllably actuates the solenoid based on the signal toadjust displacement of the pump.

In another embodiment, a hydraulic system of a transmission includes acontroller and a variable displacement pump. The pump is adapted to bedriven by a torque-generating mechanism and includes an inlet and anoutlet. Moreover, the pump is configured to generate fluid flow andpressure throughout the system. The system also includes a lube circuitfluidly coupled to the pump and a lube regulator valve disposed in thelube circuit. The lube regulator valve is configured to move between atleast a regulated position and an unregulated position, where theregulated position corresponds to a regulated pressure in the lubecircuit. A pressure switch is fluidly coupled to the lube regulatorvalve and configured to move between a first position and a secondposition, where the switch is disposed in electrical communication withthe controller. A solenoid is disposed in electrical communication withthe controller, such that the solenoid is controllably coupled to thepump to alter the displacement of the pump.

In one aspect of this embodiment, once the fluid pressure in the lubecircuit reaches a substantially regulated condition, the lube regulatorvalve moves from the unregulated position to the regulated position. Inanother aspect, the pressure switch is configured to detect the movementof the lube regulator valve between the regulated position andunregulated position and the pressure switch moves between the firstposition and the second position upon movement of the lube regulatorvalve. Related thereto, the movement of the pressure switch between thefirst position and second position induces a signal triggered to thecontroller and the controller controllably actuates the solenoid basedon the signal. In a further aspect, the pump displacement iscontrollable between a first displacement and a second displacement,where the fluid flow distributed from the outlet is adjustablycontrolled based on the pump displacement and the actuation of thesolenoid controllably adjusts pump displacement.

In an alternative aspect, the system can include a main circuit fluidlycoupled to the pump and lube circuit and a main regulator valve disposedin the main circuit. The main regulator valve is configured to movebetween at least a regulated position and an unregulated position, wherethe regulated position corresponds to a regulated pressure in the maincircuit. In addition, a second pressure switch is fluidly coupled to themain regulator valve and configured to move between a first position anda second position, where the second pressure switch is disposed inelectrical communication with the controller. In a similar aspect, thesolenoid is controllably actuates between a first condition and a secondcondition upon movement of at least one of the main regulator valve andthe lube regulator valve to its regulated position.

In yet a further aspect, the system can include a temperature sensordisposed in electrical communication with the controller. Thetemperature sensor is adapted to detect a temperature of the fluid inthe transmission. The system can also include a cooler circuit fluidlycoupled to the pump and main circuit, where the cooler circuit isstructured to receive fluid and adjust its temperature as the fluidpasses therethrough. Here, the temperature sensor is structured todetect the fluid temperature in the transmission and communicate saidtemperature to the controller. In turn, the controller controllablyactuates the solenoid from a first electrical state to a secondelectrical, where the actuation between the first electrical state andthe second electrical state adjusts the rate of fluid flow passingthrough the cooler circuit.

In a further exemplary embodiment, a method is provided for controllingfluid flow through a transmission. The transmission includes acontroller, a variable displacement pump having an inlet and an outlet,a main circuit fluidly coupled to the pump, a lube circuit fluidlycoupled to the pump and main circuit, a main regulator valve, a luberegulator valve, a pressure switch, and a solenoid. Here, the methodincludes pumping fluid from the pump into the main circuit until thefluid pressure in the main circuit reaches a first regulation point andfluidly actuating the main regulator valve from an unregulated positionto a regulated position when the fluid pressure in the main circuitreaches the first regulation point. The method also includes pumpingfluid into the lube circuit until the fluid pressure in the lube circuitreaches a second regulation point and fluidly actuating the luberegulator valve from an unregulated position to a regulated positionwhen the fluid pressure in the lube circuit reaches the secondregulation point. Moreover, the method includes moving the pressureswitch from a first position to a second position and detecting themovement of the pressure switch from the first position to the secondposition. The solenoid is actuated from a first electrical state to asecond electrical state and the displacement of the pump is adjustedfrom a first displacement to a second displacement.

In one aspect of this embodiment, the method can include controlling arate of fluid flow pumped from the outlet. The method can also includeincreasing the displacement of the pump to increase the rate of fluidflow pumped from the outlet. Alternatively, the method can includedecreasing the displacement of the pump to decrease the rate of fluidflow pumped from the outlet. In another aspect, the method includesdetecting a fluid temperature with a temperature sensor, sending asignal to the controller based on the detected temperature, andadjusting the rate of fluid flow from the pump outlet until the detectedtemperature reaches a desired temperature. In a further aspect, themethod can include triggering the pressure switch from the firstposition to the second position when the fluid pressure in the maincircuit reaches the first regulation point or when the fluid pressure inthe lube circuit reaches the second regulation point.

In an alternative aspect, the method includes moving a second pressureswitch from a first position to a second position and detecting themovement of the second pressure switch from the first position to thesecond position. Related thereto, the method can include triggering thesecond pressure switch from the first position to the second positionwhen either the fluid pressure in the main circuit reaches the firstregulation point or the fluid pressure in the lube circuit reaches thesecond regulation point. Moreover, the solenoid is actuated from thefirst electrical state to the second electrical state when either thefirst pressure switch is moved from its first position to its secondposition or the second pressure switch is moved from its first positionto its second position.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned aspects of the present invention and the manner ofobtaining them will become more apparent and the invention itself willbe better understood by reference to the following description of theembodiments of the invention, taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is an exemplary block diagram and schematic view of oneillustrative embodiment of a powered vehicular system;

FIG. 2 is an exemplary schematic of a hydraulic control system of atransmission;

FIG. 3 is another exemplary schematic of a hydraulic control system of atransmission;

FIG. 4 is a graphical representation of a leakage adaptive profile for amain circuit pressure;

FIG. 5 is a graphical representation of a leakage adaptive profile for alube circuit pressure;

FIG. 6 is an exemplary schematic of a feed forward model for controllingpump flow in a transmission;

FIG. 7 is a table of exemplary inputs to the feed forward model of FIG.6;

FIG. 8 is an exemplary flowchart of a method for controlling pump flowusing the model of FIG. 6;

FIG. 9 is a graphical representation of flow demand and flow supplycurves for a shift between ranges;

FIG. 10 is a graphical representation of a flow curve to accommodatelube flow;

FIG. 11 is a graphical representation of a flow curve based ontemperature adjustment; and

FIG. 12 is a graphical representation of a flow curve based on slipspeed across a torque converter.

Corresponding reference numerals are used to indicate correspondingparts throughout the several views.

DETAILED DESCRIPTION

The embodiments of the present invention described below are notintended to be exhaustive or to limit the invention to the precise formsdisclosed in the following detailed description. Rather, the embodimentsare chosen and described so that others skilled in the art mayappreciate and understand the principles and practices of the presentinvention.

Referring now to FIG. 1, a block diagram and schematic view of oneillustrative embodiment of a vehicular system 100 having a drive unit102 and transmission 118 is shown. In the illustrated embodiment, thedrive unit 102 may include an internal combustion engine, diesel engine,electric motor, or other power-generating device. The drive unit 102 isconfigured to rotatably drive an output shaft 104 that is coupled to aninput or pump shaft 106 of a conventional torque converter 108. Theinput or pump shaft 106 is coupled to an impeller or pump 110 that isrotatably driven by the output shaft 104 of the drive unit 102. Thetorque converter 108 further includes a turbine 112 that is coupled to aturbine shaft 114, and the turbine shaft 114 is coupled to, or integralwith, a rotatable input shaft 124 of the transmission 118. Thetransmission 118 can also include an internal pump 120 for buildingpressure within different flow circuits (e.g., main circuit, lubecircuit, etc.) of the transmission 118. The pump 120 can be driven by ashaft 116 that is coupled to the output shaft 104 of the drive unit 102.In this arrangement, the drive unit 102 can deliver torque to the shaft116 for driving the pump 120 and building pressure within the differentcircuits of the transmission 118.

The transmission 118 can include a planetary gear system 122 having anumber of automatically selected gears. An output shaft 126 of thetransmission 118 is coupled to or integral with, and rotatably drives, apropeller shaft 128 that is coupled to a conventional universal joint130. The universal joint 130 is coupled to, and rotatably drives, anaxle 132 having wheels 134A and 134B mounted thereto at each end. Theoutput shaft 126 of the transmission 118 drives the wheels 134A and 134Bin a conventional manner via the propeller shaft 128, universal joint130 and axle 132.

A conventional lockup clutch 136 is connected between the pump 110 andthe turbine 112 of the torque converter 108. The operation of the torqueconverter 108 is conventional in that the torque converter 108 isoperable in a so-called “torque converter” mode during certain operatingconditions such as vehicle launch, low speed and certain gear shiftingconditions. In the torque converter mode, the lockup clutch 136 isdisengaged and the pump 110 rotates at the rotational speed of the driveunit output shaft 104 while the turbine 112 is rotatably actuated by thepump 110 through a fluid (not shown) interposed between the pump 110 andthe turbine 112. In this operational mode, torque multiplication occursthrough the fluid coupling such that the turbine shaft 114 is exposed todrive more torque than is being supplied by the drive unit 102, as isknown in the art. The torque converter 108 is alternatively operable ina so-called “lockup” mode during other operating conditions, such aswhen certain gears of the planetary gear system 122 of the transmission118 are engaged. In the lockup mode, the lockup clutch 136 is engagedand the pump 110 is thereby secured directly to the turbine 112 so thatthe drive unit output shaft 104 is directly coupled to the input shaft124 of the transmission 118, as is also known in the art.

The transmission 118 further includes an electro-hydraulic system 138that is fluidly coupled to the planetary gear system 122 via a number,J, of fluid paths, 140 ₁-140 _(J), where J may be any positive integer.The electro-hydraulic system 138 is responsive to control signals toselectively cause fluid to flow through one or more of the fluid paths,140 ₁-140 _(J), to thereby control operation, i.e., engagement anddisengagement, of a plurality of corresponding friction devices in theplanetary gear system 122. The plurality of friction devices mayinclude, but are not limited to, one or more conventional brake devices,one or more torque transmitting devices, and the like. Generally, theoperation, i.e., engagement and disengagement, of the plurality offriction devices is controlled by selectively controlling the frictionapplied by each of the plurality of friction devices, such as bycontrolling fluid pressure to each of the friction devices. In oneexample embodiment, which is not intended to be limiting in any way, theplurality of friction devices include a plurality of brake and torquetransmitting devices in the form of conventional clutches that may eachbe controllably engaged and disengaged via fluid pressure supplied bythe electro-hydraulic system 138. In any case, changing or shiftingbetween the various gears of the transmission 118 is accomplished in aconventional manner by selectively controlling the plurality of frictiondevices via control of fluid pressure within the number of fluid paths140 ₁-140 _(J).

The system 100 further includes a transmission control circuit 142 thatcan include a memory unit 144. The transmission control circuit 142 isillustratively microprocessor-based, and the memory unit 144 generallyincludes instructions stored therein that are executable by thetransmission control circuit 142 to control operation of the torqueconverter 108 and operation of the transmission 118, i.e., shiftingbetween the various gears of the planetary gear system 122. It will beunderstood, however, that this disclosure contemplates other embodimentsin which the transmission control circuit 142 is notmicroprocessor-based, but is configured to control operation of thetorque converter 108 and/or transmission 118 based on one or more setsof hardwired instructions and/or software instructions stored in thememory unit 144.

In the system 100 illustrated in FIG. 1, the torque converter 108 andthe transmission 118 include a number of sensors configured to producesensor signals that are indicative of one or more operating states ofthe torque converter 108 and transmission 118, respectively. Forexample, the torque converter 108 illustratively includes a conventionalspeed sensor 146 that is positioned and configured to produce a speedsignal corresponding to the rotational speed of the pump shaft 106,which is the same rotational speed of the output shaft 104 of the driveunit 102. The speed sensor 146 is electrically connected to a pump speedinput, PS, of the transmission control circuit 142 via a signal path152, and the transmission control circuit 142 is operable to process thespeed signal produced by the speed sensor 146 in a conventional mannerto determine the rotational speed of the turbine shaft 106/drive unitoutput shaft 104.

The transmission 118 illustratively includes another conventional speedsensor 148 that is positioned and configured to produce a speed signalcorresponding to the rotational speed of the transmission input shaft124, which is the same rotational speed as the turbine shaft 114. Theinput shaft 124 of the transmission 118 is directly coupled to, orintegral with, the turbine shaft 114, and the speed sensor 148 mayalternatively be positioned and configured to produce a speed signalcorresponding to the rotational speed of the turbine shaft 114. In anycase, the speed sensor 148 is electrically connected to a transmissioninput shaft speed input, TIS, of the transmission control circuit 142via a signal path 154, and the transmission control circuit 142 isoperable to process the speed signal produced by the speed sensor 148 ina conventional manner to determine the rotational speed of the turbineshaft 114/transmission input shaft 124.

The transmission 118 further includes yet another speed sensor 150 thatis positioned and configured to produce a speed signal corresponding tothe rotational speed of the output shaft 126 of the transmission 118.The speed sensor 150 may be conventional, and is electrically connectedto a transmission output shaft speed input, TOS, of the transmissioncontrol circuit 142 via a signal path 156. The transmission controlcircuit 142 is configured to process the speed signal produced by thespeed sensor 150 in a conventional manner to determine the rotationalspeed of the transmission output shaft 126.

In the illustrated embodiment, the transmission 118 further includes oneor more actuators configured to control various operations within thetransmission 118. For example, the electro-hydraulic system 138described herein illustratively includes a number of actuators, e.g.,conventional solenoids or other conventional actuators, that areelectrically connected to a number, J, of control outputs, CP₁-CP_(J),of the transmission control circuit 142 via a corresponding number ofsignal paths 72 ₁-72 _(J), where J may be any positive integer asdescribed above. The actuators within the electro-hydraulic system 138are each responsive to a corresponding one of the control signals,CP₁-CP_(J), produced by the transmission control circuit 142 on one ofthe corresponding signal paths 72 ₁-72 _(J) to control the frictionapplied by each of the plurality of friction devices by controlling thepressure of fluid within one or more corresponding fluid passageway 140₁-140 _(J), and thus control the operation, i.e., engaging anddisengaging, of one or more corresponding friction devices, based oninformation provided by the various speed sensors 146, 148, and/or 150.The friction devices of the planetary gear system 122 are illustrativelycontrolled by hydraulic fluid which is distributed by theelectro-hydraulic system in a conventional manner. For example, theelectro-hydraulic system 138 illustratively includes a conventionalhydraulic positive displacement pump (not shown) which distributes fluidto the one or more friction devices via control of the one or moreactuators within the electro-hydraulic system 138. In this embodiment,the control signals, CP₁-CP_(J), are illustratively analog frictiondevice pressure commands to which the one or more actuators areresponsive to control the hydraulic pressure to the one or morefrictions devices. It will be understood, however, that the frictionapplied by each of the plurality of friction devices may alternativelybe controlled in accordance with other conventional friction devicecontrol structures and techniques, and such other conventional frictiondevice control structures and techniques are contemplated by thisdisclosure. In any case, however, the analog operation of each of thefriction devices is controlled by the control circuit 142 in accordancewith instructions stored in the memory unit 144.

In the illustrated embodiment, the system 100 further includes a driveunit control circuit 160 having an input/output port (I/O) that iselectrically coupled to the drive unit 102 via a number, K, of signalpaths 162, wherein K may be any positive integer. The drive unit controlcircuit 160 may be conventional, and is operable to control and managethe overall operation of the drive unit 102. The drive unit controlcircuit 160 further includes a communication port, COM, which iselectrically connected to a similar communication port, COM, of thetransmission control circuit 142 via a number, L, of signal paths 164,wherein L may be any positive integer. The one or more signal paths 164are typically referred to collectively as a data link. Generally, thedrive unit control circuit 160 and the transmission control circuit 142are operable to share information via the one or more signal paths 164in a conventional manner. In one embodiment, for example, the drive unitcontrol circuit 160 and transmission control circuit 142 are operable toshare information via the one or more signal paths 164 in the form ofone or more messages in accordance with a society of automotiveengineers (SAE) J-1939 communications protocol, although this disclosurecontemplates other embodiments in which the drive unit control circuit160 and the transmission control circuit 142 are operable to shareinformation via the one or more signal paths 164 in accordance with oneor more other conventional communication protocols.

In the present disclosure, a system and method is disclosed forimproving fluid flow through a hydraulic system of a transmission. Thesystem and method can be for a hydraulic control system that utilizeshydraulic and electrical control features to improve stability,efficiency, and performance of the hydraulic system. Through theseimprovements, other factors such as transmission performance and fueleconomy can be improved. Moreover, the present disclosure describes amodel-based approach for achieving improvements in the control andperformance of the hydraulic system and the transmission. Some aspectsof the present disclosure can be incorporated into downloadable andreadable software or instructions stored in the memory unit 144 of thecontrol circuit 142.

In this disclosure, the transmission control circuit 142 may beinterchangeably referred to as a transmission controller, or controller.In the event an engine control circuit is described, the engine controlcircuit may be referred to as an engine controller. In addition, fluidflow through the hydraulic system of the transmission can be describedwith respect to pressure and flow rate. Other characteristics of thefluid flow, such as temperature, may also be described. When the terms“fluid flow” is disclosed herein, it is intended to refer to the flowrate or volume of fluid flow passing through a point in the hydraulicsystem, whereas “fluid pressure” refers to the actual pressure of thefluid at a designated location in the system.

In a conventional hydraulic system of a transmission, a pump isrotationally driven by a torque-generating mechanism such as a torqueconverter. In some aspects, a prime mover or engine output mayrotationally drive the pump. The pump can be a gerotor pump, acrescent-style pump, a variable displacement pump, or any other knownpump. As the pump is rotationally driven, fluid can be collected throughan inlet or suction port of the pump. As the pump rotates, fluidpressure and flow builds and the fluid is pumped through an outlet ofthe pump and into a main hydraulic circuit, or main circuit, of thehydraulic system. The fluid passing through the main circuit has adefined pressure, referred to as main pressure. The fluid can be pumpedthrough the main circuit, and this pressure can be controlled by avalve. In this disclosure, the valve is referred to as a main regulatorvalve.

As the fluid is pumped into the main circuit, the main pressure canreach a steady-state condition. In one aspect, a solenoid can modulateor control the main pressure in the system. When there is a demand forfluid, e.g., to fill an oncoming clutch, the main pressure in the maincircuit may decrease suddenly due to the immediate demand for fluid. Themain regulator valve can react more quickly to this immediate demandthan the pump. In any event, the lack of fluid pressure in the maincircuit is detected and the pump is controlled to pump additional flowinto the main circuit. In many conventional arrangements, however, thissudden increase in fluid flow causes an undershoot or depressed mainpressure in the system. The delay between the demand and supply of fluidand then the sudden depleted supply of fluid due to the delayed responseby the pump can negatively shift quality.

To address this issue, an exemplary hydraulic system 200 is illustratedin FIG. 2. The hydraulic system 200 includes a variable displacementpump 202. The variable displacement pump 202 is a pressure-based pump,such that if pressure is regulated in the system 200, the pump 202 canoutput the necessary fluid flow as needed. In other words, if pressurein the system 200 decreases, the pump 202 increases its flow until thepressure is regulated, and vice versa. To facilitate the regulation ofpressure in the system 200, and particularly in the main circuit, a mainregulator valve 204 is disposed in fluid communication with the pump202. The main regulator valve 204 recognizes the pressure needed in thesystem 200, and particularly in the main circuit of the system 200. Inthis manner, the main regulator valve 204 acts as a feedback controlsuch that the valve 204 strokes or moves between positions untilpressure demands are met. In doing so, the main regulator valve 204 iscontrollably stroked against spring pressure exerted by a spring (notshown). The main regulator valve 204 can move to one defined positionsuch that excess fluid is directed back to the suction port of thevariable displacement pump 202. As a result, the main regulator valve204 acts as a feedback control that converts fluid flow from the pump202 into main pressure.

In FIG. 2, fluid is pumped from the outlet of the pump 202 along a mainflow path 228 to the main regulator valve 204, and fluid is directedalong hydraulic path 230 to satisfy the needs of a main circuit 206. Themain circuit 206 includes the controls (e.g., clutches) for operatingand controlling the transmission. Along the hydraulic path 230 is asolenoid 222 for modulating or regulating pressure in the main circuit206. Therefore, the fluid pressure in the main circuit 206 can beregulated by the solenoid 222. Until now, however, the fluid flow in thesystem 200 has not been regulated or controlled.

As described, the control of the variable displacement pump 202 is viathe main regulator valve 204. As the valve 204 strokes due to a pressuredemand in the system, the pump pressure “decrease” or control changesdue to the sudden demand for fluid in the system 200. The delayedresponse of the pump 202 can lead to an undershoot and overshoot of mainpressure in the main circuit, which as previously described, cannegatively impact the hydraulic system and transmission. To overcomethis problem, it can be desirable to better control when the overshootand undershoot conditions occur, and more specifically, alter orcompensate for this by inducing the pressure response under steady-stateconditions.

The variable displacement pump 202 produces fluid flow based off ofinput speed of the torque-generating mechanism and pressure. Thus, mainpressure increases or decreases as the system pressure increases ordecreases, and this is ideal under steady-state conditions. One featureof the present disclosure is compensating for the delayed time responseof the pump 202 by increasing fluid flow as soon as possible, andpreferably before there is a demand in the system due to a clutch fill,for example. Here, the supply of fluid can be initiated before theclutch fill process is initiated, thereby avoiding inconsistent clutchfill times. As such, garage shifts can be improved due to increasedflow.

To understand how the fluid flow is controllable in the hydraulic system200 of FIG. 2, a second flow path 234 and a third flow path 240 arefluidly coupled to the main regulator valve 204. As main pressure isregulated in the main circuit 206, the main regulator valve 204 canstroke to a new position to enable fluid to pass through the second flowpath 234 and into a converter circuit 208. The converter circuit 208 canbe part of the torque converter 108 as described above with reference toFIG. 1. Fluid can also pass through another flow path 236 and into acooler circuit 210. The cooler circuit 210 can have an inlet and anoutlet, and a means for regulating or controlling the temperature offluid passing therethrough.

As the converter circuit 208 and cooler circuit 210 are satisfied withfluid flow, fluid continues to be pumped via another flow path 238 andinto a lube circuit 212 of the hydraulic system 200. The lube circuit212 enables fluid to lubricate bearings, clutches, shafts, gears, etc.in the transmission. Fluid pressure in the lube circuit 212 can bereferred to as lube pressure. Similar to main pressure, the hydraulicsystem 200 can include a valve for regulating lube pressure. In thisdisclosure, the valve is referred to as a lube regulator valve 214. Thelube regulator valve 214 is fluidly coupled to the lube circuit and isdisposed in a location of the system 200 after the cooler circuit 210.

The lube regulator valve 214 can detect when the lube pressure hasregulated in the lube circuit 212. Once lube pressure reaches itsregulation point, the lube regulator valve 214 strokes or moves to adifferent position so that additional fluid is directed to a sump 226 ofthe transmission. In the embodiment of FIG. 2, the main regulator valve204 can also be in fluid communication with sump 226 where excess fluidis directed along the third flow path 240 thereto. Similarly, the luberegulator valve 214 can direct fluid along a different flow path 242 sothat excess fluid is dumped to sump 226.

Once the lube regulator valve 214 strokes to its regulated position,i.e., the position at which lube pressure has reached its regulationpoint, a pressure switch 218 can detect the movement of the valve 214 tothis position. This movement can trigger the switch 218 to toggle ormove to a different electrical state, thereby sending a signal to acontroller 216 of the transmission. As shown in FIG. 2, the controller216 and pressure switch 218 can be electrically coupled to one anotheralong a communication path 248. In this manner, the pressure switch 218acts like an input to a closed loop system in which the switchcommunicates with the controller 216. In turn, the controller 216receives the signal from the switch 218 and understands thecommunication as being an indicator that the lube circuit 212 issatisfied. As a result, extra or excess flow is not useful to thehydraulic system 200.

Once the controller 216 receives the signal from the pressure switch218, it can actuate a different solenoid 224 for controlling the pumpflow. This solenoid can be referred to as a pump control solenoid 224and is disposed along flow path 232. Flow path 232 can be fluidlycoupled with the decrease port of the variable displacement pump 202.The pump flow can be controlled by altering or changing the displacementof the variable displacement pump 202. Here, the controller 216 cancommunicate with the pump control solenoid 224 via communication link244. Thus, depending on the demands of the hydraulic system 200, thecontroller 216 can communicate with the pump control solenoid 224 toeither increase or decrease pressure at the decrease port of the pump202. This thereby increases or decreases the displacement of the pump202.

A similar approach can be done by regulating main pressure andcommunicating to the controller 216 when main pressure reaches itsregulation point. An example of this is shown in FIG. 3. Here, anembodiment of a hydraulic system 300 includes the pressure switch 218 incommunication with the lube regulator valve 214. In addition, a secondpressure switch 302 is disposed in communication with the main regulatorvalve 204. Therefore, as main pressure regulates and the main regulatorvalve 204 moves to its regulated position, the second pressure switch302 can send a signal to the controller 216 via communication link 304.With both pressure switches, the controller 216 can more accuratelycontrol the needs of the hydraulic system 300 by controllably actuatingthe pump control solenoid 224 and thereby controlling pump flow.

In an alternative embodiment, a hydraulic system may only include thepressure switch 302 disposed in communication with the main regulatorvalve 204. In a different embodiment, a second pump may be disposedeither along flow path 236 or flow path 238 to further facilitate fluidflow through the system. This second pump (not shown) may be referred toas a lube pump that can provide higher flow but lower pressure.

One of the advantages of the hydraulic control system in FIGS. 2 and 3is the ability to control fluid temperature in the system. As fluidpasses through the cooler circuit 210 it enters the lube circuit 212 andbuilds lube pressure. It is desirable to build lube pressure and satisfythe lube circuit 212 as quickly as possible. Once lube pressureregulates, it can also be desirable to maintain or control fluidtemperature passing through the different circuits. To do so, atemperature sensor 200 is disposed in fluid communication with the sump226. The temperature sensor 220 can also be electrically coupled to thecontroller 216 via communication path 246. In some instances, atransmission may operate efficiently such that the fluid temperatureoperating therein is cooler than desired. This may increase spin lossesin the transmission. In other instances, the transmission may beoperating where the fluid temperature is hot, which can negativelyimpact different hardware operating in the transmission. Therefore, anideal temperature or temperature range may be programmed into thecontroller 216 for maintaining or controlling the fluid temperature ator within the desired range.

During operation, the temperature sensor 220 can communicate a current,real-time fluid temperature to the controller 216 via communication link246. In turn, the controller 216 can controllably actuate the pumpcontrol solenoid 224 to adjust pump displacement. By adjusting pumpdisplacement, fluid flow can be controlled from the pump and through thecooler circuit 210. In other words, the pump control solenoid 224 caneffectively control cooler flow through the cooler circuit 210 until thetemperature sensor 220 detects a fluid temperature that either meets thedesired temperature or falls within the desired temperature range. Thus,if the fluid temperature is greater than a desired temperature, thehydraulic control system can increase the fluid flow through the cooleruntil the fluid temperature decreases to within a desired range.Moreover, if the fluid temperature is cooler than the desiredtemperature, the hydraulic control system can reduce fluid flow throughthe cooler circuit 210 until the fluid temperature increases. Theadjusted fluid flow through the cooler circuit 210 can be controlled bythe pump control solenoid 224 to controllably adjust the fluidtemperature operating within the transmission.

Besides controlling temperature, the pump control solenoid 224 can alsoadjust pump flow based on demand. If pressure throughout the lubecircuit 212 is regulated, the pump control solenoid 224 can reduce pumpflow so that “extra” or “excess” flow is reduced, thereby reducing spinlosses. Thus, it can be desirable for the controller 216 to know whenlube pressure and main pressure are regulated so that transmission spinlosses and efficiency can be improved.

Another aspect to this is being able to adapt to leakage in thehydraulic system. Leakage can vary from transmission to transmission,and this is particularly the case for pump leakage and leakage in thecontrols. A pump may vary due to side clearances, for example. In anyevent, the regulation point of both main pressure and lube pressure maydiffer between hydraulic systems due to the difference in leakage ofboth systems.

Referring to FIG. 4, for example, a graphical representation 400 of mainpressure as a function of input or engine speed is shown. Here, asengine speed increases, main pressure also increases. A nominal curve402 is shown as being indicative of a nominal or average hydraulicsystem. A first curve 404 and a second curve 406 are also shown wherethe nominal curve 402 is disposed therebetween. The first curve 404 mayrepresent a hydraulic system with a minimum amount of leakage, and thesecond curve 406 may represent a hydraulic system with a maximum amountof leakage.

In FIG. 4, there is a defined regulation pressure 408 that is reached ator about a specific engine speed. As engine speed increases, mainpressure also increases until it reaches the regulation point. Once mainpressure reaches its regulation point, the main regulator valve 204moves to its regulation position and the pressure switch 302 can detectthis position. The nominal curve 402 reaches regulation at a nominalregulation point 412. Similarly, the first curve 404 reaches regulationat a first regulation point 410 and the second curve 406 reachesregulation at a second regulation point 414. As shown, each curvereaches its corresponding regulation point at a different engine speed,thereby illustrating a variance 416 in leakage adaptive. As will bedescribed, a main pressure leakage adaptive constant may be determinedbased on the engine speed at which point the main pressure for ahydraulic system reaches its regulation point. As this will be a factordependent on the leakage of the system, it will be necessary for thecontroller 216 to learn and understand the leakage and restrictions ofthe system.

As previously described, engine speed may continue to increase evenafter main pressure regulates, and the main regulator valve directs theadditional fluid to the converter circuit 208, cooler circuit 210, andlube circuit 212. As lube pressure builds, it too regulates and thepressure switch 218 can detect this regulation point and send a signalto the controller 216 indicating this condition has been reached. InFIG. 5, a graphical representation 500 is shown of lube pressure as afunction of engine speed. Here, as engine speed increases, lube pressurealso increases. A nominal curve 502 is shown as being indicative of anominal or average hydraulic system. A first curve 504 and a secondcurve 506 are also shown where the nominal curve 502 is disposedtherebetween. The first curve 504 may represent a hydraulic system witha minimum amount of leakage, and the second curve 506 may represent ahydraulic system with a maximum amount of leakage.

Lube pressure continues to increase as engine speed increases, and likemain pressure, reaches its regulation point 508 at a defined enginespeed. The nominal curve 502 reaches regulation at a nominal regulationpoint 512. Similarly, the first curve 504 and second curve 506 reachregulation at a first regulation point 510 and a second regulation point514, respectively. As shown, each curve reaches the regulation pressure508 at different engine speeds, thereby indicating a variance 516 inleakage adaptive. From this, a lube pressure leakage adaptive constantmay be determined as a function of engine speed and the lube pressureregulation point for the given hydraulic system.

As shown in FIGS. 4 and 5, at a given set of conditions including enginespeed and temperature, a lube regulator valve 214 and main regulatorvalve 204 will stroke to regulated positions for a nominal hydraulicsystem. Due to leakage and variation in each hydraulic system, however,both valves may stroke to their respective regulation positions at adifferent engine speed than the nominal system. For instance, if thereis more leakage in one hydraulic system, it may take longer to buildmain and lube pressures and therefore the pressures may not regulateuntil at a higher engine speed. Alternatively, if there is less leakage,the main pressure and lube pressure may regulate quicker than thenominal system, and thus at a reduced engine speed. From the systems ofFIGS. 2 and 3, the point at which lube pressure regulates can bedetected and communicated to the controller 216. As a result, thecontroller 216 can make necessary adjustments to pump flow and otheroutputs in the system to compensate for leakage and variance in thesystem. For purposes of this disclosure, this is called leakageadaptive.

The controller can learn a leakage adaptive constant for either or bothmain pressure and lube pressure. Once the leakage adaptive constant isknown, particularly for lube pressure, the controller 216 can make thenecessary adjustments to the system and predict flows and pressures ofthe system under most conditions. Moreover, once the lube circuit issatisfied and lube pressure regulates, additional fluid pumped by thevariable displacement pump into the lube circuit 212 can be directed tosump 226. Fluid pressure and flow can be controlled under differenttransient conditions, as well as fluid temperature can be controlled byadjusting pump flow.

The controller 216 can learn and store the different regulation pointsfor each condition under which main pressure and/or lube pressureregulates (e.g., when ascending an incline, filling a clutch,cruise-like conditions, stop-and-go conditions, etc.). The controller216 can create tables and store the regulation values based ontemperature, speed, etc. As the same condition is repeated, thecontroller 216 can determine if main or lube pressure regulated at aboutthe same point as done previously. In addition, the controller 216 canoperably control the pump control solenoid 224 to command a certain flowcharacteristic or profile based on previously learned conditions. Thecontroller 216 can also determine if the pressure switch 218, 302triggered a signal thereto based on regulation of lube pressure or mainpressure. In the event the pressure has not regulated, the controller216 can continuously adapt and relearn to changing conditions. Whileleakage may or may not vary under most circumstances, temperaturevariation may cause the greatest variation or change in leakage in thesystem. The controller 216 therefore can continuously learn and adapt totemperature variation and other changes in the hydraulic system.

Another aspect to leakage adaptive is prognostic control. For a givenset of conditions, the leakage adaptive constant for either mainpressure or lube pressure should generally not change substantiallyunless there is an issue in the hydraulic system. In FIG. 5, forexample, suppose the regulation point for lube pressure is 1000 RPM fora certain condition (e.g., at a defined temperature, etc.). As thecontroller 216 continuously monitors when the pressure switch 218detects movement of the lube regulator valve 214 to its regulatedposition, the controller 216 can further detect changes in theregulation point. For instance, if engine speed continuously increasesbefore the regulation point is reached, the controller 216 may detect aproblem in the hydraulic system. A broken seal or damage to the variabledisplacement pump may cause an increase in leakage in the system,thereby resulting in the lube pressure (or main pressure) regulationpoint changing with increasing engine speed.

In the event of a possible leakage induced by a broken seal or otherproblem in the hydraulic system, the controller 216 can be programmed orinclude instructions to detect the problem. For instance, the controller216 can include instructions that indicate a threshold or thresholdrange. This threshold or range may be based on a specific engine speedat which lube or main pressure regulates. Alternatively, this thresholdor range may be based off a degree of change in the regulation point.Moreover, this threshold or range may be based off how quickly theregulation point changes (i.e., a time-based consideration). Thecontroller 216 may track the number of times the lube pressure or mainpressure regulates and detect the change in regulation point based off acount or quantity of regulation detections. The pressure switch 218provides an input to the controller 216 to detect when the lube pressureregulates and the second pressure switch 302 provides another input tothe controller 216 for when main pressure regulates. Therefore, in theexample above, if lube pressure suddenly regulates at 2000 RPM ratherthan 1000 RPM, the controller 216 can detect this and trigger an alarmor diagnostic code. Depending on the severity of the leak, thecontroller 216 may further limit the functionality of the transmissionto prevent further damage to the transmission.

A further aspect of the present disclosure is the ability tocharacterize both the fluid flow and pressure throughout the entirehydraulic system. In this aspect, a model-based hydraulic control systemcan include a learning feature to better understand the leakage in anygiven transmission or hydraulic system so that the amount of fluid flowand pressure needed under any condition can be provided withoutsubstantial delay. More particularly, the controller can predetermineleakage in the hydraulic system, and based on the amount of leakagetherein, control the output of the variable displacement pump toaccurately provide fluid flow and pressure throughout the system underany condition. In doing so, the inherent time delay or response of thepump can be overcome by compensating for leakage and geometricalrestrictions in the system. In this disclosure, the model-based approachcan be referred to as a “feed forward” model.

As previously described, the combination of the pressure switches 218,302 and pump control solenoid 224 of FIGS. 2 and 3 can allow the “feedforward” model to be incorporated into any given hydraulic system.Through the addition of the pump control solenoid 224, the main“decrease” pressure leading to the decrease port of the pump can beaccurately controlled such that, for example, if the controller predictsan upcoming shift, the controller 216 can controllably actuate thesolenoid 224 to increase pump flow before a clutch fill command isinitiated. In doing so, the increased pump flow before commanding aclutch fill can allow the hydraulic system to meet the demand of fillingthe clutch with a sufficient amount of fluid without de-stabilizing thesystem due to a lack of fluid supply and delayed time response of thepump. Moreover, many of the issues due to the undershoot and overshootof fluid flow can be avoided via this approach.

In the proposed feed forward model, the controller can receive aplurality of inputs, such as engine or input speed, transmission rangeor gear ratio, and fluid temperature (at sump). Additional inputs can bereceived or calculated based on the leakage of the system. Once certaininputs are received by the controller, the controller can learn and/orpredict the requirements for fluid flow and fluid pressure such thatmain pressure can be controlled via the main pressure solenoid 222 andfluid flow can be controlled by the pump control solenoid 224. As aresult, not only is the fluid supply accurately provided to fillclutches, for example, but the controller can also provide the accurateamount of fluid to the clutches and other locations in the hydraulicsystem to improve shift quality and leakage. This can reduce or removeexcess fluid flow that otherwise may increase spin losses in thetransmission.

The feed forward model is a characterization of the hydraulic system andmonitoring various inputs and operating conditions so that flow andpressure requirements can be predicted and controlled accordingly. Asdescribed, this can be incorporated into a closed loop control systemsuch that the controller can make adjustments to flow and pressurerequirements based on changes to system leakage and the inputs. In otherwords, the controller can operate in accordance with the feed forwardmodel by anticipating what various input values should be under a givenset of conditions, and then if the actual input value deviates from itspredicted value, the controller can continuously make adjustments to theestimated value in real-time rather than react under conventionalcircumstances.

To better understand the feed forward model approach, the controller canfirst learn and determine the leakage adaptive value for the particularhydraulic system. In FIGS. 6-7, an exemplary embodiment of a feedforward model is shown. Here, the controller (i.e., the transmissioncontroller or control unit) is a provided a means for determining aleakage constant for the hydraulic system in the form of a flow model600. The flow model 600 considers leakage and geometrical restrictionsin the different circuits that define the hydraulic system. Forinstance, the flow model 600 can characterize the leakage from a pump602 and controls 604. As shown, fluid is transferred from an output ofthe pump 602 to the controls 604, which as described above can be partof the main circuit. From the controls 604, fluid can be supplied toclutches 606.

Once the main circuit is satisfied and main pressure regulates, fluid issupplied to the converter circuit 608, cooler circuit 610, and lubecircuit 612. Once the lube circuit 612 is satisfied and lube pressureregulates, any additional fluid can be exhausted or returned to sump 614(i.e., labeled “Exhaust” in FIG. 6). This excess fluid, which is shownby arrow 626 in FIG. 6, can be referenced as “total unusable” fluidsince the main circuit and lube circuit are satisfied. In one aspect, itcan be desirable for the controller to control pump flow so as tominimize the amount of “total unusable” fluid to improve transmissionperformance. This can be controlled by controlling pump displacement viaactuation of the pump control solenoid as previously described. Inanother aspect, the leakage adaptive parameter or pump leakage factor616 can be calculated by the controller by removing this unusablequantity of fluid for a given set of conditions.

Once the controller determines that lube pressure has regulated, thecontroller can determine the leakage for the hydraulic system. As shownin FIG. 6, the pump 602 can contribute to the overall system leakage byproducing pump leakage “P” 616. Moreover, there is controls leakage “C”618, and in addition, the clutches 606 contribute both bleeds “B”620 andfill flow “F” 622. The converter circuit 608, cooler circuit 610, andlube circuit 612 each contribute flow restrictions 624 based on geometry(e.g., orifice size, bleed diameters), converter type, and convertermode.

Referring to FIG. 7, a plurality of information 700 in the form oftables can be downloaded and stored in the memory unit of thecontroller. In table 702, for example, the controller can determine therestriction value for the converter circuit 606 based on the mode ofwhich the torque converter is operating. For instance, the torqueconverter may include a lockup clutch such that the converter operatesin either a converter mode or lockup mode.

In table 704, the controller can retrieve individual restrictiondiameters for the converter circuit 606, based on either converter modeor lockup mode, the cooler circuit 608, and the lube circuit 610. Thesummation of the restrictions of the converter circuit 606, coolercircuit 608, and lube circuit 610 can provide a total restriction value624.

In table 706, the controller can retrieve bleed orifices for each clutchbased on transmission range or gear ratio. The bleeds are generallynecessary to facilitate the release or exhaust of air from the clutches.As shown in table 706, the bleed orifice area values 620 are arrangedbased on the transmission range or gear ratio, and these values 620 canbe derived from individual bleed diameters for each clutch in thetransmission. The individual bleed diameters may be retrieved from table712. In one aspect, there may be two clutches engaged for a singlerange. From the individual bleed diameters, the bleed orifice areavalues 620 in table 706 can be determined. In a different aspect, theremay be a different number of clutches engaged for a single range. Forinstance, it may be possible only clutch is engaged. Alternatively,three or more clutches may be engaged for a given range. In any event,the individual bleed diameters for each clutch can be used to determinethe combined bleed orifice area 620 for each given range or gear ratio.

In table 708, the controller can retrieve the controls leakage 616 foreach given range or gear ratio. In one aspect, the values for thecontrols leakage 616 can be predetermined and stored in the memory unitof the controller, similar to the bleed orifice area values 620. Thecontroller can retrieve additional information from table 712, includingindividual clutch fill flow 620 and fluid viscosity factors. Lastly, intable 710, the controller can retrieve a pump displacement value andthen determine the overall pump leakage factor 616. In at least oneaspect, the pump leakage factor 616 can be an overall summation of theleakage/fluid demands of each circuit or sub-system in the transmission.

To accommodate for the fluid viscosity, each of the tables in FIG. 7 mayinclude different values dependent upon various temperatures ortemperature ranges. For instance, one value may correspond to a fluidtemperature within the range of 75° C. and 90° C., whereas a differentvalue may correspond to a fluid temperature within the range of 90° C.and 105° C. There may be other variations in the values besides thosebased on fluid temperature, but fluid temperature does often impactfluid viscosity the greatest.

Pump leakage 616 can often be a big factor or component in the overallleakage in the hydraulic system. However, once the lube regulation pointis known or determined, the controller can calculate the overall leakageof the system in accordance with the flow model of FIG. 6 and thetabular information 700 of FIG. 7. The leakage adaptive parameter isbased on pump speed (i.e., input speed), fluid temperature, clutch fill,and the like. Once these are known, the flow requirements of the systemcan be determined and fulfilled as needed.

To do so, the controller can use the leakage adaptive parameter or pumpleakage factor to adjust pump displacement. This is achieved via thepump control solenoid, which as described above, can control the“decrease” pressure of the variable displacement pump. By controllingthis “decrease” pressure, the pump displacement can either be increasedor decreased. To better illustrate this process, reference is herebymade to FIG. 8. In FIG. 8, a control process is provided for controllingpressures and flow throughout the hydraulic system of the transmission.This process 800 illustrates several steps that are only intended to beexemplary, and not limiting. For instance, other methods may includemore or less steps than that shown in FIG. 8. As a result, the method orprocess of FIG. 8 is an exemplary embodiment that illustrates theoverall process of regulating pressure within the different circuit orsub-systems of the transmission so that flows and pressures can bedesirably determined based on future demand.

In FIG. 8, a first step 802 is achieved by producing fluid flow in ahydraulic system of the transmission. Here, this is generally done bythe variable displacement pump that can be integrally disposed within anouter housing of the transmission. However, as described above,alternative embodiments may include a second pump disposed before orafter the cooler circuit to provide additional flow. Other embodimentsmay include a hydraulic pump disposed outside of the transmission tofurther facilitate fluid flow in the transmission. In this example, thevariable displacement pump can produce fluid flow and pressure in themain circuit of the transmission.

In step 804, the pressure in the main circuit, i.e., main pressure, canreach a regulation point. As shown in FIG. 3, a pressure switch 302 canbe disposed in communication with the main regulator valve 204 so thatas main pressure regulates, the pressure switch 302 can send a signalalong communication link 304 to the controller 216 to alert thecontroller 216 of this condition. Moreover, once main pressure regulatesin step 804, the main regulator valve 204 can stroke to its regulatedposition so that additional fluid can be directed to the convertercircuit 208, cooler circuit 210 and lube circuit 212 in step 806.

As fluid pressure builds in the lube circuit 212, the pressure, i.e.,lube pressure, reaches a regulation point in step 808. In doing so, thelube regulator valve 214 can stroke to its regulated position, therebytriggering the pressure switch 218 to detect this position and send asignal to the controller 216 along communication link 248. At thispoint, the controller 216 has learned or determined the regulation pointin the main circuit, lube circuit, or both (e.g., in the embodiment ofFIG. 3) in accordance with step 810. Moreover, as described, thedifferent pressure switches can detect these regulation points andcommunicate this information via signals to the controller 216 in step812.

In step 814, the controller can determine a pump leakage adaptive factorbased on the regulation points, and primarily based off the luberegulation point. As described above with reference to FIGS. 6 and 7,the controller can retrieve various inputs (e.g., controls leakagevalues, bleeds, restrictions, etc.). Many of these inputs will bedependent upon temperature, range, and converter mode. The controllercan receive this type of information according to various known means,including those previously described. Once the controller has retrievedall of the input data, it can compute the pump leakage factor or leakageadaptive parameter.

As previously described, the leakage adaptive parameter is a leakageadjustment variable for the overall leakage in the transmission. Oncethe controller determines this parameter, it can input this value into apump supply equation to determine flows and pressures throughout thehydraulic system. In one non-limiting aspect, a transmission withnominal hardware may have a leakage factor of 0.091. If a transmissionhas more leakage than the nominal transmission, the leakage factor orparameter will likely adapt to a greater value, e.g., 0.105. Likewise,if a transmission has less leakage than the nominal transmission, theleakage factor or parameter will likely adapt to a lesser value, e.g.,0.085. This can be seen in FIG. 5, for example, where the nominaltransmission may have a leakage adaptive factor of 0.091 that reachesthe lube pressure regulation point 512 at a lower engine speed than the“more leakage” transmission that may have a leakage adaptive factor of0.105 and reaches its lube pressure regulation point 514 at a higherengine speed.

Therefore, a transmission that has more leakage will likely adapt to ahigher leakage adaptive parameter compared to the nominal transmission,whereas the transmission that has less leakage will likely adapt to alower leakage adaptive parameter. The leakage adaptive parameter,however, may change over time if there is additional leakage in thetransmission. For instance, if the controller determines that thedownstream pressure switch 218 toggles or moves earlier or later thanexpected, the leakage adaptive parameter will adjust accordingly. As aresult, the controller can calculate the flow demands of thetransmission under different conditions, and based on this feed forwardmodel, the controller can then optimize the displacement of the variabledisplacement pump in step 816. Moreover, as the controller calculatesthe flow demands of the transmission, the controller can operablycontrol the output of the pump control solenoid to adjust pumpdisplacement as needed.

In FIG. 9, an exemplary graphical representation 900 is provided toillustrate how the control system can adjust pump flow based on flowdemands during a shift. In FIG. 9, an exemplary supply curve 902 anddemand curve 904 are provided for a given set of conditions. Asdescribed above, there are various inputs necessary for determining flowrequirements throughout the system. This includes engine speed,transmission sump temperature, main modulation state, transmissionrange, and whether a clutch is being filled. Based on these inputs, thecontroller can calculate the supply of fluid flow from the pump based onthe following supply equation:Supply Flow(Q _(S))=(N _(E) ×PD)−KP/νwhere N_(E) is engine speed, PD is pump displacement, P is pressure, νis fluid viscosity, and K is a constant based on the leakage adaptivefactors. K can be a function of pump leakage 616, controls leakage 618,and leakage due bleed holes 620.

Moreover, the variable K can also be a function of range. The controllermay have a lookup table stored in its memory in which K is adjusted by acorrection factor on the basis of transmission range. For instance, ifthe transmission range is reverse, the variable K may be adjusted by acorrection factor of 0.01. Alternatively, if the transmission range issecond, the variable K may be adjusted by a correction factor of 0.045.Again, these correction factors can be predetermined and stored in thememory unit of the transmission controller.

In FIG. 9, the supply curve 902 is shown as having a negative slope duein part to the leakage of the pump, controls, bleed orifices, seals,etc. In a perfect flow model without leakage, the pump flow would besubstantially constant at any given speed, but the model as described inthe present disclosure can accommodate for the various leakages in thesystem. The flow demand curve 904 is also shown. At one point 910 inFIG. 9, the supply curve 902 and demand curve 904 intersect, therebyrepresenting a certain pressure at which the flow demanded is the sameas the flow being supplied. However, at another pressure represented by“P” in FIG. 9, the supply flow Q_(S) is less than the demand flow Q_(D)(i.e., difference between points 906 and 908). As shown, the pump flow906 being supplied during the shift is insufficient to meet the flowdemand 908 to fill the oncoming clutch during the shift. As such, thecontroller can calculate this demand for the clutch fill as follows:Demand Flow=31*A*√(ΔP)where A is the area of the feed orifice in the clutch and ΔP is thedifference between the pressure, P, and the return spring of the clutch.The controller therefore can determine both the fluid demand for fillingthe oncoming clutch and the fluid supply being output by the pump.

On the basis of the pump supply and flow demand equations above, thecontroller can adjust the pump supply to meet the flow demand bycontrollably adjusting the pump displacement as described in thisdisclosure. In other words, the controller can receive the necessaryinputs as described above and retrieve constants and other variables fordetermining the leakage adaptive parameter. Based on transmission rangeand temperature, the controller can obtain viscosity (as a function oftemperature) and correction factors to determine pump supply. Thus, ifthe controller determines that for a given pressure the pump supply isinsufficient for the flow demand to fill an oncoming clutch, thecontroller can controllably adjust pump displacement until the supplyflow meets the required demand flow. Stated another way, by adjustingpump displacement, the supply flow curve 902 in FIG. 9 can be movedvertically until the supply flow point 906 intersects with the demandflow point 908. With the controller being able to adjust the supply flowto meet the flow demands during a shift, the controller can effectivelyimprove shift quality and durability of the transmission.

Referring to FIGS. 10 and 11, the controller can also adjust the pumpsupply when the transmission is operating between shifts. Here, thecontroller can operate a closed loop control system by monitoring flowrequirements to satisfy the lube circuit and maintain sump temperatureat or near a desired temperature. To do so, the controller can determinehow much pressure is needed to keep engaged clutches from slipping for agiven amount of engine torque. The pressure can be regulated by the mainregulator valve, as described above, to maintain clutch capacity. Oncethe controller has determined the requisite amount of pressure, anyexcess fluid supply can be directed to the converter, cooler circuit,and lube circuit.

The controller can be programmed to determine the amount of flow that isrequired to satisfy the requirements of the lube circuit. For instance,a plurality of flow requirement values may be provided in the form of alookup table or graph. In FIG. 10, an exemplary graphical representation1000 is provided for determining flow requirements to satisfy a lubecircuit. Here, the flow requirements can be set forth on the basis of atransmission speed, i.e., input speed or output speed. The controllercan receive or determine the input or output speed of the transmission,and based on this speed, retrieve the required flow requirement to meetthe needs of the transmission lube circuit. In FIG. 10, for example, aflow profile 1002 is shown as a function of speed. The flow requirementincreases as speed increases, but at a predetermined speed, N, the flowrequirement can level off and remain substantially constant forincreasing speeds. For instance, the predetermined speed, N, may referto 1500 RPM for the transmission output speed. At 1500 RPM, the flowrequirement, Q_(L), is indicated by point 1004 on the flow profile 1002.In this instance, if the controller determines that the output speed, N,is 1500 RPM, the controller can retrieve the flow requirement valueQ_(L) from the graphical representation. If the speed is different, thecontroller can interpolate between values or pull a defined value fromthe flow profile 1002.

In addition, the controller can monitor the transmission sumptemperature, and based on this temperature adjust flow through thecooler circuit. For instance, in FIG. 11 a different graphicalrepresentation 1100 is shown of a flow profile 1102 as a function oftemperature change. The controller can continually monitor sumptemperature in accordance with the methods described herein. Moreover,the controller can be preprogrammed or have a desired or thresholdtemperature stored in its memory unit. Alternatively, the sumptemperature may be set by a vehicle operator, for example. In any event,the controller can be provided with a desired or threshold sumptemperature and make adjustments to the hydraulic control system tochange the sump temperature, as needed.

In FIG. 11, a first temperature point 1104 and a second temperaturepoint 1106 are shown along the flow profile 1102. In this embodiment,the first temperature point 1104 corresponds to a difference betweendesired and actual temperature, ΔT₁. The second temperature point 1106refers to a second difference, ΔT₂. Each of the changes in temperaturecorresponds to a different flow. For instance, the first change intemperature ΔT₁ corresponds to a first flow requirement, Q₁, and thesecond change in temperature ΔT₂ corresponds to a second flowrequirement, Q₂.

Based on the flow profile 1102 of FIG. 11, if the desired or thresholdtemperature is T_(T) but the actual sump temperature is lower than thethreshold, the controller may not adjust the supply flow. However, ifthe actual sump temperature is greater than the threshold temperature,the controller can determine the difference between the actual andthreshold temperatures. Based on this difference, the controller candetermine the flow requirement from the graphical representation 1100 ofFIG. 11 to reduce the sump temperature. This can be achieved byproviding additional flow through the cooler circuit, as describedabove.

Moreover, as described above with reference to FIG. 10, the controllercan determine the corresponding pressure for maintaining clutch capacityat a certain engine torque. Alternatively, rather than engine torque,this may be a function of accelerator or throttle pedal position. In anyevent, the controller can determine the amount of fluid being suppliedby the pump at the given pressure using the pump supply equation above.

This supply flow, Q_(S), corresponds to the amount of flow available tosatisfy the converter, cooler circuit and lube circuit. As described,the controller can then determine whether the supply flow, Q_(S), issufficient for satisfying lube, converter and cooling, and if not, thecontroller can then make adjustments to pump displacement to increaseflow in the overall system. If, based on current input or output speed,the lube flow requirement, Q_(L), is less than Q_(S) and the controllerdetermines the sump temperature is at or less than the thresholdtemperature, T_(T), the controller can make further adjustments toreduce flow and provide better fuel economy.

On the other hand, if the lube flow requirement, Q_(L), is greater thanthe supply flow, QS, the controller can controllably adjust pumpdisplacement to increase the amount of fluid supplied by the pump tosatisfy the needs of the lube circuit. In addition, if the actual sumptemperature is greater than the temperature threshold, T_(T), thecontroller can compute this difference and use the graphicalrepresentation 1100 of FIG. 11 to determine the amount of flow needed toreduce the sump temperature.

Referring to FIG. 12, a graphical representation 1200 is provided for atorque converter flow requirement. The torque converter can be asignificant heat generator, particularly during instances in which thevehicle is ascending a steep grade or repeatedly launching from a stop.As described above with reference to FIG. 1, torque multiplicationoccurs through the fluid coupling between the drive unit 102 andtransmission 118 such that the turbine shaft 114 is exposed to moretorque than is being supplied by the drive unit 102. The torquemultiplication is advantageous for transferring torque to the wheelsduring a vehicle launch, but it also tends to generate the most heat inthe torque converter. As a result, it can be desirable to remove ordissipate this heat through the cooler circuit, if possible.

The transmission controller can be used to monitor the amount of heatbeing generated by the torque converter by monitoring the amount oftorque produced by the drive unit (or engine) and detecting orcalculating the amount of converter slip. Converter slip can be definedas the ratio of input speed and turbine speed. Stated another way, theconverter slip is the speed differential across the torque converter.The controller can receive input torque from the engine or drive unitvia a datalink or signal path between the controller and drive unitcontrol circuit (e.g., engine controller). In the event the transmissioncontroller cannot receive the input torque, the controller can calculatethe input torque as a function of slip speed.

In FIG. 12, a flow profile 1200 is shown for satisfying a converter flowrequirement. Here, the controller can calculate the converter slip speedand then retrieve a desired flow from the graphical representation 1200of FIG. 12. For example, in FIG. 12, there are a plurality of definedflows along the flow profile 1202, including a first flow Q₁ and asecond flow Q₂. The first flow, Q₁, corresponds to point 1204 on theflow profile 1202 at a first slip speed, SS₁. Similarly, the secondflow, Q₂, corresponds to point 1206 on the flow profile 1202 at a secondslip speed, SS₂. It is to be understood that both slip speed values areonly two of a plurality of slip speed values. The controller mayinterpolate as necessary to determine the desired flow at a differentslip speed value. Alternatively, the controller may be programmed with aformula for the flow profile based on slip speed or input torque. In anyevent, the controller can continuously monitor the slip speed anddetermine whether additional flow is needed to dissipate the heatgeneration from the torque converter.

In addition, while only one flow profile 1202 is shown in FIG. 12, theremay be a plurality of flow profiles. Each flow profile may be related toa specific position of the accelerator pedal (i.e., throttle pedalposition or percentage). Moreover, there may be various curves dependingon the type and model of the torque converter. In the event the torqueconverter includes a lockup clutch, the controller can monitor or detectwhen the lockup clutch is engaged. When the lockup clutch is engaged,the controller can be programmed to skip the evaluation of the converterflow requirement and only determine the amount of flow required for thelube and cooler circuits.

Thus, on the basis of FIGS. 10-12, the controller can be programmed orinstructed to evaluate three flow requirements, i.e., the luberequirement, sump temperature or cooler requirement, and converter flowrequirement. In one aspect, the controller can determine which of thethree flow requirements is the greatest, and based on this maximum flow,the controller can adjustably control pump displacement to achieve thedesired amount of flow. In a different aspect, the controller may sumthe three flow requirements, calculate the average, or compute adifferent desired flow on the basis of the three flow requirements.Moreover, the controller can continuously monitor, calculate, anddetermine the three flow requirements and make real-time adjustments topump displacement based on changes to any of the requirements. Byadjusting pump displacement, the controller can effectively control thethree flow requirements as desired. In doing so, the controller can alsoimprove overall fuel economy of the vehicle.

While the flow requirements for the lube circuit, cooler circuit, andconverter are shown in FIGS. 10, 11, and 12 as graphicalrepresentations, it is to be understood that these may lookup tableswith values for the controller to retrieve. For the lube circuit, theflow required may be provided based on transmission input speed, turbinespeed, transmission output speed, torque or shift frequency. Likewise,for the cooler circuit, the flow required to reduce sump temperature maybe provided based on a plurality of temperature differences, e.g., inincrements of 1-5° C. Similarly, for the converter flow requirement, theflow required to dissipate heat generated in the converter may beprovided based on slip speed, input torque, converter model, and/oraccelerator pedal position. Once the controller determines the supplyflow and the required flow to satisfy each of the requirements of thelube circuit, cooler circuit and converter circuit, the controller cancontrollably actuate the pump control solenoid to adjust pumpdisplacement. Moreover, this can be part of a closed-loop control wherethe controller can continuously calculate and determine the flow supplyand flow demand of the system and continuously adjust pump displacementto improve fuel economy.

While exemplary embodiments incorporating the principles of the presentinvention have been disclosed hereinabove, the present invention is notlimited to the disclosed embodiments. Instead, this application isintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

What is claimed is:
 1. A hydraulic system of an automatic transmission,comprising: a controller; a variable displacement pump adapted to bedriven by a torque-generating mechanism, the pump having an inlet and anoutlet, where the pump is configured to generate fluid flow and pressurethroughout the system; a main circuit fluidly coupled to the pump; amain regulator valve disposed in the main circuit, the main regulatorvalve being configured to move between at least a regulated position andan unregulated position, where the regulated position corresponds to aregulated pressure in the main circuit; a pressure switch fluidlycoupled to the main regulator valve and configured to move between afirst position and a second position, where the switch is disposed inelectrical communication with the controller; a solenoid disposed inelectrical communication with the controller, the solenoid controllablycoupled to the pump to alter the displacement of the pump; a lubecircuit fluidly coupled to the pump and main circuit; a lube regulatorvalve disposed in the lube circuit, the lube regulator valve beingconfigured to move between at least a regulated position and anunregulated position where the regulated position corresponds to aregulated pressure in the lube circuit; a second pressure switch fluidlycoupled to the lube regulator valve and configured to move between afirst position and a second position, where the second pressure switchis disposed in electrical communication with the controller; wherein thelube regulator valve moves from the unregulated position to theregulated position once the fluid pressure in the lube circuit reaches asubstantially regulated condition; and the second pressure switch isconfigured to detect the movement of the lube regulator valve betweenthe regulated position and unregulated position, where the pressureswitch moves between the first position and the second position uponmovement of the main regulator valve; and wherein the movement of thesecond pressure switch between the first position and second positioninduces a signal triggered to the controller; and the controllercontrollably actuates the solenoid based on the signal to adjustdisplacement of the pump.
 2. The hydraulic system claim 1, wherein, oncethe fluid pressure in the main circuit reaches a substantially regulatedcondition, the main regulator valve moves from the unregulated positionto the regulated position.
 3. The hydraulic system of claim 2, wherein:the pressure switch is configured to detect the movement of the mainregulator valve between the regulated position and unregulated position;and the pressure switch moves between the first position and the secondposition upon movement of the main regulator valve.
 4. The hydraulicsystem of claim 3, wherein: the movement of the pressure switch betweenthe first position and second position induces a signal triggered to thecontroller; and the controller controllably actuates the solenoid basedon the signal.
 5. The hydraulic system of claim 1, wherein: the pumpdisplacement is controllable between a first displacement and a seconddisplacement, where the fluid flow distributed from the outlet isadjustably controlled based on the pump displacement; and the actuationof the solenoid controllably adjusts pump displacement.
 6. The hydraulicsystem of claim 1, wherein the lube regulator valve moves to itsregulated position after the main regulator valve moves to its regulatedposition.
 7. A hydraulic system of a transmission, comprising: acontroller; a variable displacement pump adapted to be driven by atorque-generating mechanism, the pump having an inlet and an outlet,where the pump is configured to generate fluid flow and pressurethroughout the system; a lube circuit fluidly coupled to the pump; alube regulator valve disposed in the lube circuit, the lube regulatorvalve being configured to move between at least a regulated position andan unregulated position, where the regulated position corresponds to aregulated pressure in the lube circuit; a pressure switch fluidlycoupled to the lube regulator valve and configured to move between afirst position and a second position, where the switch is disposed inelectrical communication with the controller; and a solenoid disposed inelectrical communication with the controller, the solenoid controllablycoupled to the pump to alter the displacement of the pump, wherein, oncethe fluid pressure in the lube circuit reaches a substantially regulatedcondition, the lube regulator valve moves from the unregulated positionto the regulated position, wherein, the pressure switch is configured todetect the movement of the lube regulator valve between the regulatedposition and unregulated position; and the pressure switch moves betweenthe first position and the second position upon movement of the luberegulator valve, wherein the movement of the pressure switch between thefirst position and second position induces a signal triggered to thecontroller; and the controller controllably actuates the solenoid basedon the signal.
 8. The hydraulic system of claim 7, wherein: the pumpdisplacement is controllable between a first displacement and a seconddisplacement, where the fluid flow distributed from the outlet isadjustably controlled based on the pump displacement; and the actuationof the solenoid controllably adjusts pump displacement.
 9. The hydraulicsystem of claim 7, further comprising: a main circuit fluidly coupled tothe pump and lube circuit; a main regulator valve disposed in the maincircuit, the main regulator valve being configured to move between atleast a regulated position and an unregulated position, where theregulated position corresponds to a regulated pressure in the maincircuit; a second pressure switch fluidly coupled to the main regulatorvalve and configured to move between a first position and a secondposition, where the second pressure switch is disposed in electricalcommunication with the controller.
 10. The hydraulic system of claim 9,wherein the solenoid is controllably actuated between a first conditionand a second condition upon movement of at least one of the mainregulator valve and the lube regulator valve to its regulated position.11. A hydraulic system of a transmission, comprising: a controller; avariable displacement pump adapted to be driven by a torque-generatingmechanism, the pump having an inlet and an outlet, where the pump isconfigured to generate fluid flow and pressure throughout the system; alube circuit fluidly coupled to the pump; a lube regulator valvedisposed in the lube circuit, the lube regulator valve being configuredto move between at least a regulated position and an unregulatedposition, where the regulated position corresponds to a regulatedpressure in the lube circuit; a pressure switch fluidly coupled to thelube regulator valve and configured to move between a first position anda second position, where the switch is disposed in electricalcommunication with the controller; and a solenoid disposed in electricalcommunication with the controller, the solenoid controllably coupled tothe pump to alter the displacement of the pump; and further comprising atemperature sensor disposed in electrical communication with thecontroller, the temperature sensor adapted to detect a temperature ofthe fluid in the transmission.
 12. The hydraulic control system of claim11, further comprising a cooler circuit fluidly coupled to the pump andmain circuit, where the cooler circuit is structured to receive fluidand adjust its temperature as the fluid passes therethrough; wherein,the temperature sensor is structured to detect the fluid temperature inthe transmission and communicate said temperature to the controller;further wherein, the controller controllably actuates the solenoid froma first electrical state to a second electrical, where the actuationbetween the first electrical and second electrical state adjusts therate of fluid flow passing through the cooler circuit.
 13. A method ofcontrolling fluid flow through a transmission, the transmissionincluding a controller, a variable displacement pump having an inlet andan outlet, a main circuit fluidly coupled to the pump, a lube circuitfluidly coupled to the pump and main circuit, a main regulator valve, alube regulator valve, a pressure switch, and a solenoid, the methodcomprising: pumping fluid from the pump into the main circuit until thefluid pressure in the main circuit reaches a first regulation point;fluidly actuating the main regulator valve from an unregulated positionto a regulated position when the fluid pressure in the main circuitreaches the first regulation point; pumping fluid into the lube circuituntil the fluid pressure in the lube circuit reaches a second regulationpoint; fluidly actuating the lube regulator valve from an unregulatedposition to a regulated position when the fluid pressure in the lubecircuit reaches the second regulation point; moving the pressure switchfrom a first position to a second position; detecting the movement ofthe pressure switch from the first position to the second position;actuating the solenoid from a first electrical state to a secondelectrical state; adjusting the displacement of the pump from a firstdisplacement to a second displacement; detecting a fluid temperaturewith a temperature sensor; sending a signal to the controller based onthe detected temperature; and adjusting the rate of fluid flow from thepump outlet until the detected temperature reaches a desiredtemperature.
 14. The method of claim 13, further comprising controllinga rate of fluid flow pumped from the outlet.
 15. The method of claim 14,further comprising: increasing the displacement of the pump; andincreasing the rate of fluid flow pumped from the outlet.
 16. The methodof claim 14, further comprising: decreasing the displacement of thepump; and decreasing the rate of fluid flow pumped from the outlet. 17.The method of claim 13, further comprising triggering the pressureswitch from the first position to the second position when the fluidpressure in the main circuit reaches the first regulation point.
 18. Themethod of claim 13, further comprising triggering the pressure switchfrom the first position to the second position when the fluid pressurein the lube circuit reaches the second regulation point.
 19. The methodof claim 13, further comprising: moving a second pressure switch from afirst position to a second position; and detecting the movement of thesecond pressure switch from the first position to the second position.20. The method of claim 19, further comprising triggering the secondpressure switch from the first position to the second position wheneither the fluid pressure in the main circuit reaches the firstregulation point or the fluid pressure in the lube circuit reaches thesecond regulation point.
 21. The method of claim 19, wherein thesolenoid is actuated from the first electrical state to the secondelectrical state when either the first pressure switch is moved from itsfirst position to its second position or the second pressure switch ismoved from its first position to its second position.